package com.wugui.datax.admin.tool.meta;

/**
 * MySQL数据库 meta信息查询
 *
 * @author zhouhongfa@gz-yibo.com @ClassName MySQLDatabaseMeta @Version 1.0
 * @since 2019/7/17 15:48
 */
public class MySQLDatabaseMeta extends BaseDatabaseMeta implements DatabaseInterface {

  private static volatile MySQLDatabaseMeta single;

  public static MySQLDatabaseMeta getInstance() {
    if (single == null) {
      synchronized (MySQLDatabaseMeta.class) {
        if (single == null) {
          single = new MySQLDatabaseMeta();
        }
      }
    }
    return single;
  }

  @Override
  public String getSQLQueryComment(String schemaName, String tableName, String columnName) {
    return String.format(
        "SELECT COLUMN_COMMENT FROM information_schema.COLUMNS where TABLE_SCHEMA = '%s' and TABLE_NAME = '%s' and COLUMN_NAME = '%s'",
        schemaName, tableName, columnName);
  }

  @Override
  public String getSQLQueryPrimaryKey() {
    return "select column_name from information_schema.columns where table_schema=? and table_name=? and column_key = 'PRI'";
  }

  @Override
  public String getSQLQueryTables() {
    return "show tables";
  }

  @Override
  public String getSQLQueryColumns(String... args) {
    return "select column_name from information_schema.columns where table_schema=? and table_name=?";
  }
}
